I think TB is correct but I had to resort to something else to set up Outlook to send messages which otherwise sat in the Outbox.
If you cannot resolve it yourself there is a Sky workaround - basically you register on Sky Users Forum. Search for a post "How to apply for a Skyuser SMTP account". Think it started back in Feb 2008.
Follow the post requirements for applying - here is the message I got back when I set it up earlier this year.
Authentication is necessary (in Outlook this is in the "Outgoing Server" tab within the "More Settings" option
You have now been setup to use the SMTP server settings as follows...
Username: as supplied (Forum Username)
Password: as supplied
SMTP Server: mail.skyusermail.com
Port: 25
Please note we do not support SSL.
If your username contains a space then the space will have been removed for the SMTP server IE: jo blogs becomes joblogs,
the password is case sensitive,
for any problems can you please use the contact us form and we will try to sort it out ASAP for you.
Terms and conditions please read carefully
By using the Skyusermail SMTP server you agree to the following..
visit
http://www.skyuser.co.uk/forum/skyuser-mail-smtp/ section from time to time to be kept up to date on news, service details and updates.
Any breach of these terms and conditions will result in the following..
etc etc